Clearing Transforms Doesn't Make Rest Pose (IK problem?)
As I told you, there's a difference between the Rest and Pose position of the bones because of the fact that the IK bones will stick to their controller as soon as you switch to Pose mode, and if the controller head is not placed exactly where the IK bone's tail is placed, it will make the IK jump. How to fix it?

First select the IK bone and make all the other ones invisible. Then select its tail and press ShiftS to put the 3D cursor on the same position.



Then unhide everything and this time make only the controller visible. As you see the controller's head is not at the exact same position as the 3D cursor:



So press ShiftS in order to put the selection on the 3D cursor:



Now when you'll switch from Rest to Pose they won't be any difference (actually there's still a bit difference because of the target position, you can fix that by making sure that the target is well aligned with the IK.

As a side note, always bend the elbows and the knees a bit so that Blender knows how to bend it when you switch to Pose mode: